Railway Science (Physics-Electric Current and its Effects) (Part-II)

Resistance in series: When two or more resistors are joined from end to end, then the resistances are connected in series. In series resistance circuit, the same current passes through each of them, when some potential difference is applied across the combination. The potential difference is the sum of potential differences across all the individual resistors. In a series combination of resistors, the potential difference across any resistor is proportional to its resistance while the current in the circuit is independent of the relative position of the various resistors in the circuit.

Magnetic field lines are a visual tool used to visualize the direction and the strength of the magnetic field. The direction of the magnetic field is taken to be the direction in which a north pole of the compass needle moves inside it. Therefore it is taken by convention that the field lines emerge from the north pole and merge at the south pole.

A stationary magnetic field has no effect on a wire or current loop while a moving or changing magnetic field does produce a current in a current loop or a voltage across the ends of a current loop. The induced potential difference depends upon the number of turns and the rate of change of magnetic flux with time. The rate of change of magnetic flux depends upon the speed of the approach of the magnet and the magnetic moment of a magnet. The induced current depends upon the resistance of the coil.

The phenomenon of Electromagnetic induction is involved. (a) 0 to 50 s: the current in A is steady - In this case the galvanometer will not be deflected, means current will not be induced in B.

An electrical fuse is a safety device that operates to provide protection against the overflow of current in an electrical circuit. Fuse wire should have low melting point, high conductivity and least deterioration due to oxidation. Under normal conditions, the fuse wire is a part of the circuitry, contributing to a complete loop for current to flow through it. However, when an excessive amount of current flows through the fuse wire, the heating effect of the current causes the fuse wire to melt.

AC generators work on the principle of Faraday’s law of electromagnetic induction, which states that electromotive force – EMF or voltage – is generated in a current - carrying conductor that cuts a uniform magnetic field. The generated EMF depends on the number of armature coil turns, magnetic field strength, and the speed of the rotating field. The part of an AC generator in which the voltage is produced is known as an armature.

If Four wires of the same material are connected like beads of a garland that means they are connected in series so let if resistance of each wire is R then, The equivalent resistance of the garland will become R + R + R + R = 4 R (four times).

Electric motors are used as an important component in electric fans, refrigerators, mixers, washing machines, computers, MP3 players etc. A galvanometer is used to detect and measure a current in an electric circuit. A galvanometer consists of an iron core within a rectangular loop of wire. In order to convert a galvanometer to a voltmeter, a high resistance is connected to it in series.

The magnetic field inside a solenoid (B) = µI N / L. Here, B is the magnetic field, N is the number of turns in the solenoid, I is the current in the coil, L is the length of the coil and µ is the permeability of free space.

The magnetic field due to a long straight infinite current carrying conductor is inversely proportional to its distance from the conductor. As the distance increases, the intensity of the magnetic field decreases